This invention relates to a method of quantitatively analyzing a target substance, such as a harmful substance, contained in a liquid or a gas using a quartz oscillator and to a device therefor.
A gas analyzer using a quartz oscillator as a sensor is known (JP-A-08-233759, JP-A-10-038784 and JP-A-10-090152). The quartz oscillator has a lipid membrane capable of immobilizing a target substance contained in a fluid. Upon absorption of the target substance, the oscillation frequency is changed due to an increase of the weight of the lipid membrane. Thus, by detecting the change in frequency of the quartz oscillator, it is possible to determine the concentration of the target substance in the fluid. The conventional analyzer, however, has a drawback because the sensitivity of the sensor is not able to be changed. Thus, it has been hitherto necessary to concentrate or dilute the fluid so that the concentration of the target substance in the fluid falls within a range suitable for being detected by the analyzer.
It is, therefore, an object of the present invention to provide a method which can precisely analyze a concentration of a target substance contained in a fluid without need of any pretreatment, such as concentration or dilution, of the fluid, even when the concentration is extremely high or low.
Another object of the present invention is to provide a device for analyzing a concentration of a target substance contained in a fluid, which permits the control of the sensitivity thereof.
In accomplishing the foregoing objects, there is provided in accordance with one aspect of the present invention a method of analyzing a concentration of a target substance contained in a fluid, wherein said fluid is contacted with a quartz oscillator having a surface covered with a layer capable of absorbing the target substance so that the target substance is absorbed by said layer to cause a change in frequency of said quartz oscillator, and wherein said change in frequency of said quartz oscillator is detected to determine the concentration of said target substance, characterized in that said fluid and said quartz oscillator are controlled to have substantially the same temperature, and in that said temperature is selected so that said quartz oscillator has a desired sensitivity.
In another aspect, the present invention provides a method of analyzing a concentration of a target substance contained in a fluid, comprising the steps of:
(a) providing a quartz oscillator having a surface covered with a layer capable of absorbing the target substance;
(b) maintaining each of said fluid and said quartz oscillator at substantially the same predetermined temperature selected according to the concentration of the target substance in said fluid;
(c) contacting said fluid having said predetermined temperature with said layer of said quartz oscillator having said predetermined temperature, so that the target substance is absorbed by said layer; and
(d) detecting a frequency of said quartz oscillator during step (c).
In a further aspect, the present invention provides a device for analyzing a concentration of a target substance contained in a fluid, comprising:
a contacting chamber;
a feed passage for feeding the fluid into said contacting chamber;
means disposed in said feed passage for adjusting a temperature of said fluid at a desired predetermined temperature;
a discharge passage for discharging the fluid from said contacting chamber;
a quartz oscillator disposed in said chamber and having a surface covered with a layer capable of absorbing said target substance, so that the fluid introduced through said feed passage into said chamber is contacted with said layer; and
means for detecting a frequency of said quartz oscillator.